Geology
I. Overview

The MBNMS spans nearly 10,000 km² in the central California region,
and extends offshore an average distance of approximately 50 km (a maximum
distance of nearly 100 km in the Monterey Bay area and a minimum distance
of 15 km off Partington Point) between the Farallon Islands in the north
and Morro Bay in the south (Figure 1). It contains
one of the world's most geologically diverse and complex seafloors and continental
margins. The MBNMS is located on a plate boundary which separates the North
American Plate from the Pacific Plate, and is marked by the San Andreas
fault system. This is an active tectonic region with common occurrences
of earthquakes, submarine landslides, turbidity currents, flood discharges
and coastal erosion. It is also a region of extensive natural and economic
resources.

The Santa Cruz and Gabilan mountain ranges dominate the topography in the
northern and central half of the region. Two major rivers (San Lorenzo and
Pajaro Rivers) and a major creek (Scott Creek) enter Monterey Bay from these
highlands through well defined valleys (Figure 1).
Elkhorn Slough, an old river estuary that today is occupied only by tidal
salt marshes, extends inland from Moss Landing for more than 10 km. The
broad, extensive Salinas Valley and the northern Santa Lucia Range are the
dominant topographic features in the southern half of the region; the Salinas
River is the major drainage system (Figure 1).
South of Monterey, the west flank of the Santa Lucia Range drops abruptly
into the ocean. Here, the valleys of the Carmel and Little Sur Rivers are
dominant topographic features. From Point Sur to Morro Bay many streams
and creeks drain the southern Santa Lucias and cut the steep western face
of the mountain range.